Leaves are drooping and turning yellow/purple

Man it seems everything went perfectly for about two months and now all I have is problems. My plants' leaves are turning yellow, which doesn't seem all that abnormal, but today is seems they've advanced further into yellowness than is usual for one day. Also there is some purple coming on a few of them that looks pretty disturbing.

Worst of all, many of them are drooping right now. They look terrible, I tried to get the best pictures I could. It's hard to really see the yellowness, but you can see the purple ok. The drooping isn't on the whole plants, just some of the leaves, mostly the yellow ones.

I changed the res two days ago and put in all the same stuff as normal, except for I added Adv. Nut's Overdrive at a little under full strength. I backed off a bit on some of the other stuff as well. My PPM right now says it only ~1200, so it seems fine. Any ideas?

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Well I'm not a hydro guy but if you problem started after you added that new shit thats probably it. Also I thought most the time people would work their way up to half strength and avoid full strength. I would clear the res and put in just ph'd water for a week or so just to see if it helped...but I don't really know what the fuck I'm talking about just seems like it would be something you added.

my leaves are turning yellow on inside and are droopin on my bigger one

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You might want to start a new thread LOL. This one is six monthes old.
Yellow is lack of nitrogen. Either there is none available, or the Ph is such that the plant cannot use it. And when the purple sets in too thats nitrogen and phosphorus def. Droopy leaves is from water stress. Too much or too little.